Catalytic Slow Pyrolysis of Rice Husk Pellets with Rice Husk Ash Catalyst Using Macro-TGA: Apparent Kinetics and Product Characterization

This research introduces a novel biomass-catalyst interaction approach in the catalytic pyrolysis process. The use of in-situ catalytic pyrolysis, where the catalyst is directly added to biomass followed by pelletization to enhance the quality of gas and bio-oils, remains underexplored. This method facilitates better contact between the biomass and the catalyst, leading to altered decomposition mechanisms and selective product formation. The study focused on the pyrolysis of rice husk pellets, using rice husk ash as a catalyst. Catalytic slow pyrolysis was analyzed in terms of apparent kinetics and product characterization through a self-designed macro-thermogravimetric analysis. The pellets were heated from 303 to 873 K at a rate of 10 K/min in an N2 atmosphere. Gas was collected and analyzed using the GC-TCD method at various temperature intervals during pyrolysis. Additionally, bio-oil and char were analyzed with GC-MS and FT-IR methods. The findings revealed that a single-stage multi-component kinetic model effectively described the pyrolysis reaction. The ash slightly accelerated the decomposition rates of hemicellulose and lignin but inhibited cellulose decomposition. The catalytic effect of the ash was more pronounced at higher temperatures. The gas composition was predominantly CO and CO2, with CH4 and H2 becoming detectable at temperatures above 723 K. The addition of ash increased the concentrations of H2, CH4, and CO2, while reducing CO levels. Furthermore, the ash reduced the corrosiveness of bio-oil by decreasing oxygenates and acids, thereby enhancing its energy density due to an increase in light phenolics and monocyclic aromatic hydrocarbons. Future research should focus on improving the catalytic activity of husk ash to further optimize its role in pyrolysis processes.